Electric power sources and electric motors in which inverter circuits having high energy-conversion efficiency are used, as well as hybrid cars, electric vehicles, and other apparatuses to which such electric power sources and electric motors are applied, are being introduced at an increasing rate as an approach towards lowering societal exposure to carbon. In these fields, rectifier diodes, power MOSFETs, IGBTs, thyristors, and the like, which are referred to as power semiconductor elements, are used in high-current control. There are cases where power semiconductor elements are individually incorporated into a circuit substrate; additionally, semiconductor modules in which a plurality of power semiconductor elements are integrated in a single package, or an intelligent power module (IPM) that is modularized with including control circuits, drive circuits, protection circuits, and the like, are also used.
Although power semiconductor elements are designed to reduce on-resistance, the amount of generated heat in accordance with high power output inevitably increases, and there are also fields in which a transition has already been made from air-cooled to liquid-cooled devices. In particular, it is preferable for semiconductor modules in which a plurality of power semiconductor elements are mounted to be of the liquid-cooled type from the standpoint of cooling efficiency due to the high amount of generated heat. However, when semiconductor modules are of the liquid-cooled type, circulation pumps, secondary coolers, and other auxiliary equipment is added, increasing the number of components; therefore, it is necessary to make the individual components as compact as possible. In particular, because the mount space for use in an electric vehicle is limited, making the semiconductor module and cooler more compact is one of the highest-priority problems.
In making the cooler more compact, it is most important to optimize the structure of partition walls and cooling fins installed in flow paths through which refrigerant is caused to flow; however, it is also important to reduce the size of the assembly required for attaching the cooler to a base.
Cited documents 1-4 disclose securing methods for securing a cooler to a semiconductor module by fastening using screws.